The objective is a collaborative effort to duplicate the positive results obtained by Barnett and colleagues (Ultrasonics Intitute, Sydney, Australia) for sister chromatid induction by high intensity pulsed ultrasound. Our previous efforts in this area have not been able to duplicate the results obtained by Barnett and collaborators. Two biological systems are proposed for use--both have yielded positive effects for SCE induction by exposure to pulsed ultrasound as reported by Barnett and collaborators; these systems include in vitro CHO cells and in vivo developing chick embryonic retinal cells. Barnett will participate in the study, to be conducted in Rochester under the exposure conditions used in Sydney to obtain positive results. All experiments will be conducted doubled blind. If a positive effect is obtained, then the physical mechanism(s) causing the effect will be investigated and will include in particular assessments for the role of acoustic cavitation. The results obtained should be directly relevant to assessments of the potential for pulsed ultrasound to induce biological effects in human tissue. Because the proposed project focuses first on replication of a previously reported positive effect and, if verification is achieved, will seek to understand the physical mechanism causing the effect, the results from this project may be extrapolated to broader questions of health and safety from exposure to diagnostic ultrasound.